Chief Executive Carrie Lam Cheng Yuet-ngor and two top aides - Secretary for Security John Lee Ka-chiu and Police Commissioner Chris Tang Ping-keung - each received a letter with white powder yesterday on Lam's 64th birthday.
It is understood that the police headquarters in Wan Chai received the letter for Tang yesterday at about 10am, while the government headquarters in Admiralty received two letters for Lam and Lee in the afternoon at about 3pm.
The chief executive's office and the Security Bureau said they called in the police after staff found the letters contained suspicious powder.
After officers with the police's explosive ordnance disposal bureau examined the letter to the police chief, the powder was understood to be flour with no danger. It is understood there were some Chinese words on the letter, but they were written ungrammatically and disorderly.
The letter did not mention any demands or threatening messages.
The letter was also a bit wet and some powder had melted.
Police also investigated the letters to the city's leader and security chief, and found that the letters have the same content as the one to Tang.
Some powder, believed to be flour, had also melted.
Police said the case has been classified as suspicious object found and officers with the Central and Western district crime unit are investigating the case.
No arrest has yet been made.